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|This page contains historical information. It is probably no longer true.|
Uploaded image and media files for Wikimedia's wikis appear on the separate subdomain upload.wikimedia.org.
upload.wikimedia.org is handled by the PowerDNS geobackend, which CNAMEs it to upload.pmtpa.wikimedia.org, upload.knams.wikimedia.org or upload.yaseo.wikimedia.org, depending on the location of the querying resolver.
Uploads have a separate set of squid proxy caches from the text squids; this avoids contention between the two data sets, which have different characteristics for object size, update rate, etc.
|ms1||/mnt/upload5||uploaded images and texvc-rendered images|
Some not-too-horrible stanza snipped from upload-settings.php:
'apaches' => array( 'pmtpa' => array( 'ms1.wikimedia.org', '=ms4_thumbs'=> 'ms4.wikimedia.org', ), ),
Thumbnails are served by ms4.
Wikimedia's wikis are configured to defer most image scaling/rasterization operations ($wgGenerateThumbnailOnParse off), just putting "optimistic" URLs <img> tags and letting a 404 handler on the thumbnail server deal with making sure the images are in place.
This does a couple nice things:
- Less interaction between primary servers and NFS
- Encapsulation of thumbnailing/scaling problems on the "image scaling cluster" so the entire grid doesn't go down due to runaway 'convert' processes etc.
These backend scalers produce the rendered images and save them back to NFS, and they also get served back out to the requesting user-agent none the wiser.
Note that thumb.php can be accessed directly from the web as well on the regular "text" Apaches. Ideally we shouldn't do that? :)
Our private wikis do not serve their files to the public through this interface; they're served through img_auth.php on the local domain, which enforced authentication.
Most of our wikis have a rewrite rule to redirect requests from /upload and /math on the primary wiki domain to the appropriate subdirectory on upload.wikimedia.org. This provides compatbility for old direct image links from the days before the separate image hosting.
Special:Filepath can also send redirects here.